I'm not sure I fully understood whether you were asking whether there is an RF output of the current cable channel or whether you can get all the analogue terrestrial channels as well, but the V+ box does have an RF output.
As long as you do not use the HD output (which disables all other outputs, likely because of copy protection and such) you can use the RF output of the box along with the SCART or composite outputs. Therefore, you can use the system in the same way you do now and watch cable upstairs.
However, you will not be able to get channels 1,2,3,4 and 5 at the same time from the box itself (it only outputs the current viewed cable channel) but you will be able to get the cable channel you are watching from the RF out.
So yes, you can output the current cable channel from the RF output. What you wont get is the analogue terrestrial channels as well (which will be going off eventually anyway) unless you hook up an aerial or other source of them (there is an antenna in port on the V+ box, which then forwards the channels out the RF out, for distribution around the house)
Hope this helps